REPRODUCTION OF COSCINASTERIAS. 



119 



a group of shorter rays. In the same months of 1915-1918, the 

 percentage was 80.4, a sufficiently good agreement. This is about 

 the maximum percentage of regenerating, or recently divided, 

 individuals encountered during a twelve-month period. From 

 Fig. 2 it is evident that the highest percentage of intact speci- 

 mens not recently divided occurred during December to March 



50 

 TO 

 60 

 50 

 40 

 50 



ao 



10 



cQ 



LU 





cx: 

 UM 



a 



o 



-3 U. *-* ^ ^ -} ^> ^ 



FIG. 2. The average percentage of Coscinasterias not showing evidence of 



_- recent self-division, during each month (191518). 



the percentage then rather rapidly sinking to a minimum dur- 

 ing midsummer. 



There is a certain correlation between the course of the curve 

 of self -division (Fig. 2) and that of temperature-variation in 

 the sea water. I reproduce here a seasonal temperature graph 

 derived from figures given by Verrill (1902), together with the 

 averages of my own data ; the curves agree rather well, in spite 

 of the fact that my temperature readings were not very numerous, 

 nor systematically taken, but were obtained mainly for different 

 special purposes having to do with other problems. 



In comparing Figs. 2 and 3, it must be recalled that the " curve 

 of self-division " is non-quantitative in one important respect : the 

 percentages of dividing animals include data derived from indi- 



